In modern electrochemistry, microelectrodes have been recognized for their special properties. In particular, the high mass flux at the electrode surface, steady-state current due to three-dimensional diffusion, low cell time constant and low ohmic potential drop properties have made them very attractive for use in electroanalytical chemistry. The major disadvantage in using microelectrodes in electrochemistry is the low current level available therefrom. For example, a microdisk electrode having a 10 micrometer diameter will give a steady-state current of only about 1.5 nanoamps in a solution of 1 mM Fe(CN).sub.6.sup.-3.
Currents at these levels are vulnerable to interferences of electrical noise and accordingly require sophisticated measuring instrumentation. This vulnerability can be overcome by the use of microelectrode arrays which maintain the special properties of microelectrodes, but provide an increase in attainable current level.
There have been several attempts to make various kinds of microelectrode arrays. Most of these attempts have compromised the feature of steady-state current.
The failure of most of the attempts to obtain a steady-state current comes from the fact that either the individual electrodes themselves exhibit only virtual steady-state current because of their size, such as microband electrodes, or the disks are randomly dispersed with separations therebetween that are too small causing current shielding.
There have been attempts in using microdisk electrode arrays with relatively large separations between the disks, but this requires handling of individual single microwires in turn causing random separation. Therefore, steady-state current is compromised due to either the large individual electrodes or the small ratio of spacing to disk dimension.
The use of minigrids as an electrode is well-known in the art. For example, the use of a minigrid in an electrode assembly is disclosed in the Senda et al U.S. Pat. No. 4,820,399. A further example of the use of a minigrid as an electrode is disclosed in Mark, Jr. et al U.S. Pat. No. 4,310,400. The Mark device uses a minigrid auxiliary electrode mounted concentric to a thin layer electrode assembly
Accordingly, there is a need for a sturdy microelectrode comprising a microdisk electrode array with ordered, relatively large separations between the disks. Further, there is a need for an electrode assembly that can maintain steady-state current at levels in the range of nanoamp or higher to provide adequate measurements for use in electroanalytical chemistry.